Sarge85:
Starting a PBEM is very easy. In the option Multiplayer Email games one can set the conditions, the players and create the game.
The difficulty is the speed of playing and keeping up the game. Usually there are not more that six players. I am in one PBEM with 4 players and we do 3 -4 turns per week, and other of 6 players and we do 4-5. In this last one we are at the beginning and the spirit is high, so everybody plays fast, but we'll see in future. With a good rate of 4 turns/week a game of 400 turns can last 100 weeks = 2 years!! I don't have experience in long games with humans, but i'm afraid they don't last so much. For what i've read they usually finish in domination or conquest.